Is there a way to have a conditional requirements.txt file for my Python application based on platform?

You can add certain conditional requirements after a semi-colon particularly useful for sys_platform and python_version.

Examples:

atomac==1.1.0; sys_platform == 'darwin'
futures>=3.0.5; python_version < '3.0'
futures>=3.0.5; python_version == '2.6' or python_version=='2.7'

Apparently you can also exclude particular versions of a library:

futures>=3.0,!=3.0.5

They are defined in PEP 508 and PEP 0345 (Environment Markers) but the syntax appears to follow the draft PEP 0496.

You could create an install.py script and call pip by script.

import pip

_all_ = [
    "SOAPpy>=0.12.22",
    "pycrypto>=2.6.1",
    "suds>=0.4",
    "Python-ldap>=2.4.19",
    "paramiko>=1.15.2",
    "nose>=1.3.4",
    "selenium>=2.44.0",
    "bottle>=0.12.8",
    "CherryPy>=3.6.0",
    "pika>=0.9.14",
]

windows = ["wmi-client-wrapper>=0.0.12",]

linux = ["WMI>=1.4.9",]

darwin = []

def install(packages):
    for package in packages:
        pip.main(['install', package])

if __name__ == '__main__':

    from sys import platform

    install(_all_) 
    if platform == 'windows':
        install(windows)
    if platform.startswith('linux'):
        install(linux)
    if platform == 'darwin': # MacOS
        install(darwin)

Another way to resolve this issue using only requirements files should be using inheritance of requirements

requirements.txt

SOAPpy>=0.12.22
pycrypto>=2.6.1
suds>=0.4
Python-ldap>=2.4.19
paramiko>=1.15.2
nose>=1.3.4
selenium>=2.44.0
bottle>=0.12.8
CherryPy>=3.6.0

windows.txt

-r requirements.txt
WMI>=1.4.9

linux.txt

-r requirements.txt
WMI>=1.4.9

Then you can call just the requirement equivalent to platform.

pip install -r windows.txt
pip install -r linux.txt

You can add additional requirements to any package after a semicolon. You may limit any package with multi-condition by and, or. more conditions: https://www.python.org/dev/peps/pep-0508/#environment-markers

examples:

futures>=3.0.5; python_version < '3.0'
futures>=3.0.5; python_version == '2.6' or python_version=='2.7'
futures>3 ; python_version >= "3.6" and sys_platform == "linux"
futures>3.3 ; python_version >= "3.6" and sys_platform == "darwin"